Portable mixer



FIG. 1 is a perspective view of a portable mixer showing my new design;

FIG. 2 is a front elevation view;

FIG. 3 is a side elevation view;

FIG. 4 is a rear elevation view;

FIG. 5 is a top plan view; and,

FIG. 6 is a bottom plan view. 

The ornamental design for a portable mixer, substantially as shown. 